In metallic telephone loops, a variety of faults occur from time to time which must be detected, located and repaired. Specifically, these faults can comprise one sided faults or two sided faults. One sided faults are where either the tip or ring of a pair of conductors in a cable is either open or shorted to a ground. Two sided faults are where both the tip and ring of the pair are shorted together or to ground, or they are both open. These faults may result from manufacturing irregularities or, more usually, from physical damage which occurs during cable usage.
The article entitled "Locating Cable Faults", by C.A. Maloney, IEEE Transactions on Industry Applications, July/August 1973, pages 380-394 (particularly pages 385 and 386) is representative of prior art techniques utilized to locate resistive shunt faults. The conventional techniques, and usual variations thereon, employ bridge-type measurements to yield voltage outputs which are a measure of the electrical distance to the fault. With a bridge measurement, craftsperson interaction is required to manipulate bridge controls to effect a balanced bridge condition. Such procedures, while satisfactory for some present day applications such as fault localization activities, are not compatible with the need to reduce the amount of manual work necessary to operate, administer and maintain networks by automating the flow of work from the time a customer reports trouble to the time service is restored.
Specifically, almost half of the cost of each circuit is used in the administration of the equipment, trunk and facilities operations. Clearly, a reduction in the amount of manual work required to test a circuit and improvement in the productivity of field craft personnel will help to reduce these high costs.